Moment formation

Fig. 1. Modified periodic table showing the itinerant vs. localized character of unsaturated transition shells. Bonding is contrasted to magnetic moment formation, to illustrate the band-like vs. atomic-like behaviour of wavefunctions. The dashed region represents the crossover between the two situations (from Ref. 1)...

However, no fingerprint such as a final state multiplet structure, as expected for fully localized 5 f electron and found in Am metal, is observed. The localization of 5 f-states is only weak (band-narrowing and widthdrawal from hybridization) in 6-Pu. This in fact is also consistent with the absence of a magnetic moment formation in 6-Pu (rather, a spin-fluctuation regime is observed ). 

In our view (Mott 1972b), mixing the bands increases the tendency to moment formation and to Mott-Hubbard insulation, because, while U is... 

We should like to derive a threshold ratio of for the formation of a local moment. By consideration of Fig. 20-20, you may establish a condition on diC/dn at the cro.ssing (in this case at n = n" = 5/2), which will indicate moment formation. Evaluate the critical (7x/r, Do the parameters of Tables 20-4 and 20-5 fail to predict a local moment as they did for iron with the parameters for Fig. 20-20,a ... 

Wachter ( ) have presented a very clear example of this behaviour in their studies of the moment formation in TmSe Te under pressure where both mixed valency, or intermediate valence (IV), and semiconductor to metal transition are found. The particular interest of this case is not only that these materials have been extensively characterized, but also because they show, from comparison of valences determined by two different experimental methods, that a unique picture which considers only one type of... 

Boppart, H. and Wachter, P., Moment Formation in Solids, W.J.L. Buyers, Ed., Plenum Press, New York, 1984, 229. Wohlleben, D., Moment Formation in Solids, W.J.L. Buyers,... 

TYPES OF MAGNETIC ORDER AND UNDERLYING MICROSCOPIC INTERACTIONS 232 Intra-atomic interactions and moment formation 232... 

Few materials show up the limitations of the two extreme viewpoints of magnetic moment formation in transition metal systems ( localized or itinerant ) more than do their intermetallic compounds. In some compounds, e.g., the (non-integral) magnetic moment may vary from one type of site to another and the moment associated with a particular transition metal atom is often different in its different compounds. The interest in the wide variety of properties exhibited by intermetallic compounds stems as much from the opportunity they offer for the understanding of magnetism in metallic systems at a fundamental level as from the possibility of producing materials of technological importance. 

The current view of these and of the off-stoichiometric (Fe0 5 Co0 5), >,Ti y alloys seems to be that they can be correctly represented by an itinerant part which is well-described in terms of the SEW model of weak-itinerant ferromagnetism but that there is additional moment formation associated with Fe or Co atoms on Ti sites (antistructure atoms) in the region of 0 < x < 0.35 leading to localized effects (Buis et al. 1981b). Parviainen (1982) has shown that the observation of a negative... 

On the other hand, lack of any anomaly in the temperature dependence of C, p, and the lattice parameters around the TN value could be taken as an argument for a non-magnetic low-temperature state (at least in zero magnetic field). Furthermore, the positive magnetoresistance at low T might reflect the influence of a magnetic field on the moment formation (fig. 4.3). 

In spite of the absence of any quasistatic moment formation, CeCee must be considered not far from magnetic ordering. Neutron data (Regnault et al. 1987) found dynamic short-range AFM correlations below 10K. Since no effect is seen on the pSR relaxation rate, the fluctuations of the moments must remain in the fast dynamical limit. Similarly magneto-resistance (Qnuki et al. 1985) and thermoelectric power (Amato et al. 1987) show anomalies at low temperature that point towards incipient magnetism. The possibility of magnetic order below 5mK has been pointed out (Schuberth et al. 1995, Pollack et al, 1995). 

Penney, T., 1984, in Moment Formation in Solids, ed. W.J.L. Buyers (Plenum Press, New York). 

Volume 117—Moment Formation in Solids edited by W. J. L. Buyers... 

The electronic-pressure formula, eq. (48), may be easily modified (Andersen et al. 1979, Eriksson et al. 1989b, c) to include the effects of moment formation in the 5f states. If the number of spin-up and spin-down electrons are denoted by n, and the fractional occupations by /, = n, /[2(2/ -H 1)], the total fractional occupation number and moment are given by... 

In eq. (41), d(/)fg destri s (creates) a d(/) electron with spin o on site i. The hq)ping is restricted to the nearest neighbors and scaled as t=t l2y/D. Ug is the screened onsite Coulomb repulsion for the localized f states and V is the hybridization between d and f states. This model retains the features of the impurity problem, including moment formation and screening, but is further complicated by the lattice effects. 

Institute on Moment Formation in Solids, Plenum, New York 1984, from Reim etal. [18]. -... 

A reasoning similar to that given above can-also be applied to Co (and Ni) compounds. Here we have to take into account that the 3d moment formation in Co and its compounds is much more vulnerable. Arguments have been presented elsewhere (Buschow et al., 1980) that the 3d moments in Co intermetallics are less localized than those in Fe intermetallics. The detrimental effect on the 3d moment formation of increasing 3d-H contacts at the expense of 3d-3d contacts upon charging is much stronger and overcompensates the beneficial influence of the reduced hybridization of the 3d electrons with the d and s, p electrons of the R component. 

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